Field
The described embodiments relate to techniques for synchronizing clocks in electronic devices in a wireless network.
Related Art
Many modern electronic devices include a networking subsystem that is used to wirelessly communicate with other electronic devices. For example, these electronic devices can include a networking subsystem with a cellular network interface (UMTS, LTE, etc.), a wireless local area network interface (e.g., a wireless network such as described in the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard or Bluetooth™ from the Bluetooth Special Interests Group of Kirkland, Wash.), and/or another type of wireless interface. In order to reduce power consumption when there is no information being wirelessly communicated, these electronic devices often transition the networking subsystem to a standby mode.
However, if the networking subsystem in an electronic device is in standby mode for too long, the clock in the electronic device may lose its synchronization with the clock in another electronic device in a wireless network. As a consequence, the electronic device may routinely re-synchronize its clock with the clock in the other electronic device.
For example, an electronic device that communicates with an access point in a wireless network using a communication protocol that is compatible with an IEEE 802.11 standard (which is sometimes referred to as ‘Wi-Fi’) may wake up its radio periodically to receive a beacon frame with synchronization information (such as a timestamp) at beacon transmission times. After receiving the beacon, the Wi-Fi radio in the electronic device may use the synchronization information to synchronize the radio clock. In addition, the Wi-Fi radio may check the Traffic Indication Map (TIM) element for data for the electronic device that is buffered at the access point.
In practice, it can be difficult to synchronize electronic devices in the wireless network in this way. In particular, in busy environments, the probability of not receiving the beacon is high. As a consequence, the Wi-Fi radio in the electronic device may stay in an active mode longer while waiting for the beacon, which may not arrive due to interference. Moreover, if the Wi-Fi radios in multiple electronic devices wake up to receive the beacon at a beacon transmission time and the beacon indicates there is buffered data for these electronic devices, the electronic devices may poll the access point for the buffered data at the same time, thereby contending with each other for access-point resources.
Furthermore, because of the risk of losing synchronization with the access point and waking up the Wi-Fi radio at the wrong time if the electronic device is in standby mode too often or if it stays in standby mode too long, the electronic device may wake up the Wi-Fi radio frequently.
Therefore, the existing synchronization technique in wireless networks may result in the electronic device staying in the active mode more often. This increases the power consumption and reduces the operating time of the electronic device, which can frustrate users and degrade the user experience.